Diabetes mellitus is a complex disease which affects up to 5% of the human population. Its primary clinical symptom is abnormally high levels of plasma glucose. The regulatory hormones that control glucose homeostasis are derived from the pancreatic islet cells. The long term goal of this grant proposal is to understand the role of basic helix-loop-helix transcription factors (bHLH) in islet cell development. In the last few years major progress has been achieved toward identifying genes (especially transcription factors) important for islet development. It was shown that Pdx1, Pax4, Pax6, Is11 and BETA2/neuroD were important transcription factors necessary for the proper islet development. Beta2 is a bHLH transcription factor that was isolated in our laboratory and was shown to be important for the insulin gene regulation. Mutation of this gene disrupts proper islet morphogenesis and eliminates the formation of two types of enteroendocrine cells: secretin and cholecystokinin producing cells. The animals develop severe diabetes and die within 3-5 days after birth. These results establish the importance of BETA2 gene in cell fate determination of enteroendocrine cells and in the islet development. Another important bHLH factor, neurogenin 3, has been isolated recently and shown to be expressed in an overlapping manner is that of BETA2 in pancreatic islet. Our preliminary data also indicated that it regulates the activity of the BETA2 promoter, thus it is likely that neurogenin 3 is upstream of the BETA2 gene in controlling the islet development. In this proposal we propose experiments to determine the upstream signals that regulate the expression of the BETA2 gene and to answer questions regarding the role neurogenin 3 plays in pancreas development. Results from this study, together with what we already know, should help us in defining the interplay between various basic helix-loop- helix and other transcription factors in pancreatic islet development.